For making a high quality and high contrast liquid crystal color display, a black matrix having excellent light screening properties must be formed between the pixels having three colors of a color filter. In particular, the black matrix of a liquid crystal color display of active matrix drive system must also have high light screening properties. This prevents image quality deterioration which accompanies a current leak due to the light of a thin film transistor (TFT). Widely used black matrices are generally obtained by the photolithographic patterning of chromium that has been deposited, for example, by sputtering. Because of the use of a thin film of chromium, this method provides black matrices having high light-screening properties and good pattern accuracy. However, this method is costly because it requires a vacuum thin film deposition step such as sputtering, or the etching waste from the etching system gives rise to a safety problem.
Methods for producing black matrices without using chromium include a method comprising patterning a resist film having dispersed therein a black pigment (e.g., carbon black) or a black dye by photolithography. This method is less costly and safer than the method using chromium. However, the resist containing a black dye or pigment does not provide sufficient resolving power. Also, sufficient light screening properties are hard to obtain.
JP-A-6-75110 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a method utilizing electroless plating. The method provides a black matrix having high light screening properties that is provide by a precipitated metal. A problem associated with this method resides in the co-existence of a metallic compound of the metal to be precipitated and a reducing agent in the electroless plating bath. This makes the bath unstable and therefore leads to increased maintenance cost.
JP-A-4-32802 discloses a method which includes the reduction of a silver salt. The method comprises coating a substrate with a silver halide emulsion, exposing the emulsion layer through a mask, and developing and fixing the exposed area corresponding to a black matrix pattern to reduce and precipitate silver. The incurred cost is relatively low, but the method cannot escape the problems arising from the emulsion layer which remains in the unexposed areas. That is, the emulsion layer tends to become colored in the heat treatment for paneling, or suffers from the generation of wrinkles or cracks when transparent electrodes are formed.